This invention relates to a valve device for controlling the intake airflow of an internal combustion engine, and in particular, to an electromagnetic flow-control valve suitable for controlling the airflow by-passing the throttle valve of an automobile gasoline engine in order to control the idle speed of the engine.
In an automobile engine, the idle speed thereof greatly influences the exhaust-gas condition and the fuel consumption. Whether the idle speed is sufficiently stabilized at a predetermined value is an important factor in an automatic-transmission-type automobile from the viewpoint of preventing "creep" (an advance of a vehicle under the idle condition). In view of this, a so-called ISC (idle-speed controller) has come into common use. The ISC measures the engine speed and effects electrical feedback control of the intake airflow by-passing the throttle valve in such a manner that the measured engine speed converges on a predetermined target figure.
The ISC needs a valve device which controls the above-mentioned intake airflow by-passing the throttle valve by means of an actuator (an electromechanical converter for valve drive). The rotary-valve devices disclosed in Japanese Patent Laid-Open No. 62-75046 and U S. Pat. No. 4428356 are examples of such valve devices. In these prior art devices, air leakage when the valve is in the completely closed position is restrained to a minimum degree, thus providing a satisfactory controllability.
The above prior art devices have such a problem that a sticking of the rotary-valve member and a need for setting valve-opening characteristics with respect to the rotation angle of the rotary-valve member are not taken into consideration. Furthermore, no particular consideration is given to a possibility of connecting the valve member for controlling the intake airflow with the actuator for driving it. As a result, these prior art devices need to require a relatively complicated construction.